Seasonal movement of Oak Burr panel??

[Sawdust=manglitter]

With this TV cabinet/sideboard i’ve been making (link below) I’m planning on using oak burr panels for the cabinet doors.

tv-cabinet-sideboard-t110601.html

I wont be ready to do the doors for a few weeks, but i’m just thinking ahead. I had a pretty big oak burr which i cut the slices from, so these panels are 10mm thick. The photo below shows one of the panels alongside the stock i have earmarked for the frame of the door.

My question is, how much should i expect oak burr to move seasonally? Would it be less than a standard straight grained plank of wood as the grain is denser and in all directions?

Thinking ahead i am... the burr wasnt quite as wide as i would’ve liked as i was limited by the capacity of my bandsaw so the burr is around 303mm wide, which compared to the wood i have earmarked for the frame of the doors would mean i currently only have around 5mm each side of the panel to fit into grooves which doesnt seem much to me. So can i get away with that, or do i need wider stock for the door frames to account for more movement?

 

[profchris]

Hard to say! I'd guess maybe 4mm of movement between dry air and humid air, but that's only a guess.

I'd suggest putting it roughly where the finished item will live, and measuring its width on a crisp winter's day when the heating has been on for some hours. That's likely to be as narrow as you will see. If the frame allows 3mm expansion either side I'd be surprised if that wasn't enough.

To be sure you could leave it in a damp shed for a couple of drizzly days and measure again, but it could well warp so I wouldn't.

 

[Beau]

I dont know you could cut a thin veneer of it and test it in the extremes measuring it's expansion and shrinkage with a vernier gauge. I thin slice will react quickly to changes in humidity.

 

[custard]

This style of construction, using a solid burr as a panel, is a signature at the Barnsley Workshops,

The photo doesn't show it very well, but there's a pronounced cushion moulding worked right across the front face of the burr to signal that it is indeed worked from the solid and is not a veneer.

Regarding your specific question, don't worry about movement. As long as the burr has been allowed to thoroughly air dry it's no more problematic than solid timber. In fact the random nature of grain direction in a burr probably makes it less prone to serious movement.

Good luck!

 

[Sawdust=manglitter]

Thanks all for the advice. Maybe that’s put my mind at ease a bit then, so hopefully I should be fine with the panel size and frame I’ve got then. The burr, I’m told, had been air drying for 15 years before I bought it and i’ve only cut two 10mm slices from the exposed bit, so seemed pretty dry before I brought it into the house to acclimatise (which was a couple of weeks ago, and will probably be another month before I get onto making the doors).

Custard, I have the lignomat as you did, what’s your experience of checking the moisture content of dense burrs? With the grain and density varying so much i’d imagine that you could end up with varied false readings? So would you take an average reading as being correct?

I do love the look of that door in your photo too. I can’t hope for mine to look as good as that, but in terms of making it look like an obvious burr, i’m tempted not to fill any of the cracks and voids and leave one natural corner empty with a void into the cabinet which I think would look quite nice. Also both slices were cut back to back, so will be kinda bookmatched at each end of the cabinet, which I know may also make it look more like veneers, but will hopefully look quite nice anyway. I know it’s not exactly going to be to a professional’s standards, but i’ve enjoyed the process and the learning curve.

 

[Racers]

If you do decide to fill any voids knots etc pound shop epoxy and instant coffee works well.

Pete

 

[stuartpaul]

If you do decide to fill any voids knots etc pound shop epoxy and instant coffee works well.

Pete

Second that, - it works really well!

 

[Sawdust=manglitter]

Thanks both. I have been filling burr voids with pigment powders and west systems epoxy, but may try coffee next time

 

[custard]

Custard, I have the lignomat as you did, what’s your experience of checking the moisture content of dense burrs? With the grain and density varying so much i’d imagine that you could end up with varied false readings? So would you take an average reading as being correct?

For measuring burrs I set the Lignomat to a specific gravity of 0.60. That's a bit lighter than most European Hardwoods but it seems to be a good average for burrs.

Here's an Oak burr that's ready to be worked, it reads 11.9% and that measurement is fairly consistent across the entire burr, falling within a range of about 11.7% to 12.3%.

Conversely here's an Elm burr that needs to dry for another year or two.

I wouldn't get too fussy about all this, in practise I can tell the Elm isn't yet ready just by picking it up, it feels too heavy, more like a tropical timber. But if you want some reassurance then the Lignomat set at 0.60 is a good way to go, you should be targeting about 12% moisture, it won't fall much below that no matter how long you leave it.

Incidentally, I've also been told many times by timber yards that a particular burr has had ten or more years drying...very occasionally that's even been true!

 

[Sawdust=manglitter]

Thank you for the tips Custard, much appreciated